Proximity switches are usually utilized in place of limit switches for sensing the proper passage of an object adjacent a sensing face the switch when inertialess sensing is desired. Proximity switches conventionally include a rotatable sensing head of generally cubical shape on which the sensing face is located. The head is rotatable on a base assembly about one axis to any one of four quadrants to bring the sensing face into a corresponding quadrant, where it can sense the object, after the base assembly is mounted on an appropriate support.
The base assembly mounting arrangement is preset or predetermined for many locations and the rotatable positioning of the head, whose sides are generally coincident with the side perimeter walls of the base assembly provides some versatility in permitting objects in any one of the four quadrants or planes to be sensed irrespective of the preset mounting arrangement.
To extend the versatility of the proximity switches and permit sensing objects passing transverse or perpendicular to the one axis or in a fifth plane, recent proximity switch designs such as shown in U.S. Pat. No. 4,314,310 incorporate a two part sensing head in which one support or base part is rotatable about the one axis and a second or sensing part having the sensing face is rotatable with the one part and relative the one part about a second axis extending at 45.degree. to the first axis.
Rotation about the second axis brings the sensing face on the sensing head into the fifth plane extending perpendicular to the one axis for sensing objects adjacent the sensing face end of the switch.
A number of problems are presented in these types of arrangements since electrical connections must be extended from the base assembly through the first or support part of the sensing head to sensing apparatus located in the second or sensing part adjacent the sensing face for transmitting signals and/or power to and from the sensing apparatus. In the usual case wires are simply strung from the base assembly through the first part to the sensing apparatus. The wires and/or their terminals are however subject to strain if rotated or twisted either too far or without constraint and this situation is further complicated if it is desired to extend numerous connections and/or it is desired to replace the sensing head to provide a different sensing mode, since sensing may be provided inductively by a coil, photo-electrically by a cell and lamp arrangement or a zero force shutter, for example.
Slip rings and brushes have conventionally been used in prior so called four-way proximity switches however these have not been either readily adaptable for five-way sensing, replacement of the sensing head for different types of sensing modes or capable of ensuring connections in the dusty and contaminated atmosphere in which such switches are often used.
It is also desirable that the sensing head be firmly secured in whatever position to which the head has been rotated. Usually a plurality of retaining screws are used to secure the head and different screws are used for each axis of rotation thereby contributing to the possibility of a failure to tighten the screws and to the expense of the installation.
Other problems relate to the spacial arrangement of the support part and sensing part of the sensing head in a five-way proximity switch, since the confines of the parts are limited but must accommodate the sensing apparatus with electrical connections, and a pivot support between the parts together with securing means therefor.